In the context that in recent years various biosensors utilizing singular catalytic action of enzymes have been developed and are undergoing clinical trial applications, demand exists for biosensors capable of making rapid and highly accurate measurements.
Taking glucose sensors as an example, today when there is a marked increase in the number of persons afflicted with diabetes, the measurement and management of blood sugar require extremely complicated steps if blood were to be centrifuged to make measurements of the plasma as done traditionally and there is a demand for a sensor capable of making measurements from whole blood.
As a simple type, there is one, similar to the test paper used in testing urine, of using a stick-shaped support and placing thereon a medium containing an enzyme reacting only to a sugar (glucose) and a dye which changes at the time of enzyme reaction or due to the products of enzyme reaction. The method is to drip blood on this medium and to measure changes in the dye after a given period of time, either with the naked eye or optically, but there is much hindrance from colored substances in the blood and the accuracy is low.
On one hand, there are proposals for devices which, including the electrodes, can be thrown away after each measurement, but while making measurement operations extremely simple, from the standpoint of electrode materials, such as platinum, and their structure, they cannot avoid becoming very expensive devices. Also, while sputtering method or vapor deposition method can be used for manufacturing the platinum electrodes, they will be very expensive to manufacture.
As a throw-away method including the electrodes, a biosensor was proposed in the Laid Open Patent Application SHO 61-294351. This biosensor, as shown in FIG. 9, has an electrode system 30 (30'), 31 (31') and 32 (32') formed from such material as carbon by a method such as screen printing upon an insulating base 37, and after forming an insulating layer 33, the electrode system is covered by a multi-apertured medium 35 holding an oxidoreductase and an electron receptor, and the whole is unitized with a support 34 and a cover 36.
When a sample fluid is dripped onto the multi-apertured medium the oxidoreductase and the electron receptor held by the multi-apertured medium are dissolved by the sample fluid, enzyme reaction proceeds between the substrates in the sample fluid and the electron receptor is reduced. After the reaction is completed, the reduced electron receptor is electrochemically oxidized and the substrate concentration within the sample fluid is obtained from the value of oxidization current at that time.
In the above noted measurement, a given voltage is provided to the sensor's electrode system, the current flowing between the electrodes is measured, and the substrate concentration in the sample fluid is calculated on the basis of this signal.
In prior art structure such as that given above, wasteful measuring work occurred such as inserting the throw-away sensors backwards and even making measurements with sensors inserted backwards. Hence, there is desire for a simple sensor and easily manipulated biosensor device to simply, rapidly and highly accurately measuring specific components within a biological specimen such as blood.